Anisotropic conducting body and method of manufacture

ABSTRACT

A layer of the mixture that contains polymer and conductive particles is applied over a first surface, when the mixture has a first viscosity that allows the conductive particles to rearrange within the layer. An electric field is applied over the layer, so that a number of the conductive particles are aligned with the field and thereafter the viscosity of the layer is changed to a second, higher viscosity, in order to mechanically stabilise the layer. This leads to a stable layer with enhanced and anisotropic conductivity.

TECHNICAL FIELD

The invention concerns a production method for forming an anisotropicconducting polymer body, such as a film or mat, comprising conductivepaths of particles in the polymer matrix. The matrix can be an adhesiveand be used for joining surfaces and connecting them electrically.

BACKGROUND OF THE INVENTION

Materials of electrically conductive polymer can be based on the mixtureof polymer matrix and conductive particles embedded into the matrix orinto an inherently conductive polymer.

In the former case the polymer matrix can be an adhesive and theelectrically conductive particles metal or metal oxide or carbonparticles such as carbon nanotubes (CNTs). The materials can also bedirectionally conductive. An electrically conductive material willusually also be thermally conductive. Wiedemann-Franz law states thatthe ratio of the electronic contribution to the thermal conductivity andthe electrical conductivity of a metal is proportional to thetemperature. For other materials the relationship is more complex.

The electrically conductive polymer films are usually produced by mixingthe filler material with a polymer resin and in order to have aconductive mixture the amount of filler material shall exceed thepercolation threshold. Mixed systems have limited lifetime and must beremixed prior to use.

In order to increase signal transmission capability without having toincrease the amount of conductive filler material conductive films aremade anisotropic. Anisotropic films can also be designed so that theyhave insulating properties in certain directions.

In EP 1809716 is described a method for making a directionallyconductive adhesive based on CNTs. A tape having an insulation base anda parallel arrangement of CNTs acting as electrical contact points ismade by growing carbon CNTs on a material used in the tape or arrangingCNTs on the tape before adding the adhesive part to the tape.

In U.S. Pat. No. 5,429,701 is described how electric interconnectionbetween discreet individual conductors of soft magnetic metal in twolayers is achieved by adjoining the conductors by a conductive adhesive.The adhesive have particles of soft magnetic metal and by applying amagnetic field the particles can be gathered in an area between theconductors.

It is known that dipolar rigid asymmetric particles or molecules can bealigned by an electric field; this is especially used for smallmolecular weight liquid crystals.

In these cases material having permanent dipole moments is fluid innormal conditions, which makes electric field alignment possible.

Aligned structures of infusible conductive carbon particles, like CNTs,are known to be formed by chemical vapour deposition or spinning.

A method for the directional growth of CNTs is shown in U.S. Pat. No.6,837,928. CNTs are grown in an electric field that directs their growthand thus leads to aligned CNTs when the growing procedure is completed.

Electric field alignment of carbon nanocone (CNC) material has beendemonstrated in Svåsand et al. Colloids & Surf. A Physicochem. Eng.Aspects 2007 308, 67 and 2009 339 211. In these articles it is shownthat nanocone material dispersed in silicon oil can form micron sizenanocone “fibres” when a field of minimum 50 V/mm is applied. In orderto form fibres within a reasonable time fields of 400V/mm is used.

In Schwarz et al. Polymer 2002, 43, 3079 “Alternating electric fieldinduced agglomeration of carbon black filled resins” is reported howcarbon black filled resins below zero-field percolation threshold canform electrically conductive networks when a field of 400 V/cm isapplied between copper electrodes dipped into the resin. This result hasbeen reproduced by Prasse et al. Compos. Sci. Tech. 2003, 63, 1835.

US 20090038832 describes a method for forming an electrical path havinga desired resistance from a mixture of carbon and metallic nanotubesdispersed in a curable polymer matrix. Electrodes are placed in contactwith the dispersion and electrical energy is applied until the desiredelectrical resistance is reached. A pure semi-conducting connection canbe achieved by burning away metallic nanotubes that may be part of thecarbon nanotube mixture, by applying a current after the deposition. Thepolymer matrix is cured in order to fix the device. Essentially sameresult has been achieved using copper particles in US20030102154A1.

A disadvantage with the method is that carbon nanotubes are veryexpensive and difficult to produce on an industrial scale. A dispersionof nanotubes is difficult to store and require specific manufacturingsteps like homogination or sonication prior to application of thedispersion to the substrate and electrode.

These methods are dedicated to the use of microelectronics and circuitboards. Moreover, they aim at connecting the alignment electrodes sothat the alignment is a step-wise procedure where the alignmentelectrodes are connected to the material and remain in the end product.

DESCRIPTION OF THE INVENTION

The invention provides for a method for forming an anisotropicconductive body, such as a film, or mat, comprising a matrix mixed withconductive particles and subsequent stabilization of the matrix. Boththermal conductivity and electrical conductivity is described herein bythe terms conductive and conductivity.

The term film includes free-standing film, below 1 cm, made of one ormore layers, comprising one or more conducting layer of the presentinvention. The term film also includes a thin layer attached to at leastone substrate, used to make e.g. the surface of a body conductive, or tomake a conductive layer within a laminate. If the film is made from anadhesive polymer, the present invention can be used as conductive glue.Films can also be used for making electrostatic discharge (ESD) devices.

The term mat includes structures above 1 cm of thickness made of one ormore layers, comprising one or more conducting layer of the presentinvention. The term mat also includes a layer attached to at least onesubstrate, used to make e.g. the surface of a body conductive, or tomake a conductive layer within a laminate. If the mat is made from anadhesive polymer, the present invention can be used as conductive glue.

The conductive particles are infusible conductive particles such ascarbon particles, metal or metal oxide particles. The conductiveparticles show low molecular or particle anisotropy and thus the majorpart of the conductive particles has low aspect ratio; aspect ratioranges of 1-4, or 1-5, 1-10 or 1-20 are typical. The terms “lowmolecular or particle anisotropy” and “low aspect ratio” has the samemeaning herein. This is the case with spherical carbon black (CB) ordisk-like or conical carbon particles here referred to as carbonnanocones (CNC). The conductive particles can be a mixture of differentcarbon particles. Also other conductive particles can be used, likemetal, such as silver or metal oxide particles or colloidal metalparticles.

The matrix can be a polymer system of any kind and it can contain one orseveral components. In particular, it can be a thermoset polymer systemwhich means that the matrix is originally fluid but can be solidified bycross-links. This polymer can be an adhesive. It can also be athermoplastic polymer system which means that the polymer is solid orviscous at lower temperatures but can be reversibly melted orplasticised by rising the temperature. It can moreover be a lyotropicpolymer system which means that the polymer matrix can be plasticised bysolvent and solidified by evaporating this solvent off. It can also beany combination of these systems. For example, the thermoset polymersystem can contain solvent for plasticizing it but the stabilization canbe based primarily on cross-linking and only secondarily on the solventevaporation.

The adhesive can be ultraviolet light (UV) curing adhesives, also knownas light curing materials (LCM). UV curing adhesives have rapid curingtime and strong bond strength. They can cure in as short times as asecond and many formulations can bond dissimilar materials and withstandharsh temperatures. These qualities make UV curing adhesives essentialto the manufacturing of items in many industrial markets such aselectronics, telecommunications, medical, aerospace, glass, and optical.Unlike traditional adhesives, UV light curing adhesives not only bondmaterials together but they can also be used to seal and coat products.

When exposed to the correct energy and irradiance in the required bandof UV light, polymerization occurs, and so the adhesives harden or cure.The types of UV sources for UV curing include UV lamps, UV LEDs andExcimer Flash lamps.

Laminates can be built up with successively applied UV cured layers.This obviates the need for adhesive or primer layers. Thin layers can beformed in very short time, in the range of one second. There are a widevariety of UV curable vinyl monomers, particularly acrylics, with a widevariety of properties that can be combined by means of copolymers orlaminates. For example strong acrylics can be combined with the fractureresistant acrylates. Acrylics could be combined with intermediate layersof cross-linked elastomers for maximizing tear strength while retainingsurface hardness. Certain fluoracrylates are hard, and antireflective.They have higher specular transmission than a commonly usedfluoropolymer, because fluoroacrylates can be completely amorphous andhave no scattering centers. Epoxy resins have tightly linked adhesivepolymer structures and can be used in surface adhesives and coatings.Such epoxy resins forms cross-linked polymer structures that have strongadhesion and low shrinkage.

There are many systems available for UV curing an adhesive, coating orfilm. The Dymax Heavy-Duty UV curing Widecure™ Conveyor Systems is anexample of a system mounted on a conveyor belt. Dymax BlueWave LED PrimeUVA used LED light and thus use less effect and have constant highintensity.

An element of the invention is that conductive paths can be formed ofpredominantly low aspect ratio particles like CB or CNC particles andthe formation can take place at low electric field strengths. Thissimplifies the production equipment and enables both larger surfaces andthicker films to be produced. The CB and CNC particles are considerablycheaper than the carbon nanotubes and can be produced in sufficientquantities by industrial methods. Moreover, it is more difficult to formuniform dispersions with carbon nanotubes than CB and CNC.

Another element of the invention is that formation of conductive pathscan take place at low electric field strengths. This simplifies theelectric equipment and the handling of films and substrates. This meansthat no specific safety aspects related to the high voltages arerequired.

The electric field can be in the order of 0.01-20 kV/cm or 0.1-5 kV/cm,or 0.1 to 1 kV/cm. This means that for alignment distance in the rangeof 10 micrometer to 1 mm the voltage applied can be in the range of10-2000 V. The field is an alternating (AC) field. A typical field is anAC field has a frequency of 10 Hz to 10 kHz. High frequencies >1 kHz arerequired for the smaller particle size <1 micrometer. Direct (DC)electric field or very low frequencies <10 Hz lead to asymmetric chainformation and build up, which can nevertheless conduct current.

The direction of the electric field can be predetermined by theelectrode arrangement and thereby the direction of the electricconnections formed by the aligned conductive particles can becontrolled.

It is also possible to heal aligned conductive particle pathways; if theconductive pathways have become defect or not properly aligned in thefirst step, the alignment step can be rerun for the case that thestabilization step of the matrix is not yet performed or if thestabilization step is reversible. This has the advantage that forexisting films under preparation of the connections the process need notto be started afresh.

The manufacturing of anisotropic conductive films does not require thatthe film forming polymer-particle mixture is in contact with theelectrodes. The manufacturing process can be conducted in a continuousway or step-wise. The anisotropic film can be attached to a substrate orbe a free-standing film; or it can be attached to one electrode, thusforming a semi-free-standing film. The electric field can be createdbetween electrodes that can be placed either in direct contact with oneor both sides of the polymer film layer or outside additional insulatinglayers, where the insulating layers are placed either in direct contactwith the film layer or not.

Another element of the invention is that the concentration of conductiveparticles may be low. For conductive mixtures a percolation threshold isdefined as the lowest concentration of conductive particles necessary toachieve long-range conductivity in the random system. In a system formedby a method according to the invention the concentration of conductiveparticles necessary for achieving conductivity in a predefined directionis not determined by the percolation threshold and the concentration canbe lower. For practical reasons the concentration of particles isdetermined by the requirements on the conductive paths, there usuallybeing no reason to have excess amounts of conductive particles notarranged into the conductive paths. The concentration of conductiveparticles in the polymer matrix could be up to 10 times lower than thepercolation threshold or even lower. Concentrations of conductiveparticles may be in the range of 0.2-10 vol %, or 0.2-2 vol %, or0.2-1.5 vol %.

This has several advantages in that mixtures having only small amountsof conductive particles are less prone to macrophase separation and arethereby easier to store. Also the mechanical strength of the anisotropicconductive film is increased if the amount of particles can be reduced.For UV cured films the curing process is more effective when the amountof particles which may shield the UV light is lower. Likewise thetransparency of a film can be increased if the amount of particles canbe reduced. A lower amount of conductive particles is also a cost-savingelement.

In an embodiment additional steps to remove most or the entire matrixafter alignment to yield distinctive, aligned molecular wires of theconductive particles are made. The removal can be done for example byexcess heating (e.g. pyrolysis) or by chemical treatment (e.g. selectivesolvent).

In another embodiment the formation of conductive paths is performeddirectly on an electrode in order to increase the surface structure ofthe electrode.

The use of the present invention includes: electrostatic discharge (ESD)devices, conductive glue and adhesives for use in solar panels andelectronics. Advantages include a low fraction of conducting material inthe matrix, as conductivity is achieved below the percolation thresholdand this gives mechanical and optical properties closer to that of theused polymer without the conductive particles. Also the process ofapplying an electrical field and using UV curing is easy to add to anexisting manufacturing process, so that using the present invention as aconductive adhesive can be done an amendment to an existing productionline.

LIST OF DRAWINGS

FIG. 1 show optical micrographs of assemblies of 0.2 vol-% CNC particlesdispersed into the adhesive (A) and aligned by the electric field (B) aswell as the schematic of the situation (C)

FIG. 2 plots the dependence of DC conductivity of 0.2 vol-% CNCparticles dispersed into the adhesive against the alignment time. Thesolid line is guide to the eye.

FIG. 3 shows aligned film with (A-B) and without (C-D) electricalcontacts between electrodes

FIG. 4 shows schematics of the UV curing technique.

FIG. 5 shows optical micrographs showing the healing of a scratch.

FIG. 6a-c shows aligned and cured conductive particle polymer system inin-plane geometry.

FIG. 7 shows aligned material with arbitrary alignment geometry andarbitrary electrode shape.

FIG. 8 shows an optical micrograph of aligned and cured film of nanoconeadhesives in in-plane geometry after pyrolysis.

FIG. 9 illustrates the steps to produce aligned conducting.

FIG. 10 illustrates dendritic structures maximizing the contact areabetween conductive item and matrix.

DETAILED DESCRIPTION OF THE INVENTION

The present invention will be described below with reference to examplesand figures. It is to be understood that the present invention is by nomeans limited to these examples and figures.

The method can be used in a production line for ESD (electrostaticdissipation or discharge, also known as antistatic) devices, such asfilms for antistatic packaging or antistatic mats or boards. A thermallyconductive film can also be made, that can e.g. be used for lightingreflectors or electronic parts, or a thermally conductive mat that e.g.can be used for form a heat sink. The method comprises the followingsteps:

-   -   i. a matrix is formed from epoxy mixed with conducting        particles, according to the present invention    -   ii. the matrix is applied to a substrate e.g. by spraying,        pouring or dipping    -   iii. an electrical field in the range of 0.01 to 20 kV/cm is        applied    -   iv. the matrix is cured, using e.g. UV light or heat    -   v. optionally the matrix is reduced, so as to expose the        conducting pathways    -   vi. optionally steps ii to v is repeated to create several        layers, e.g. for creating conductive pathways in different        directions.

The method can also be used in a production line for e.g. solar cells orelectronics. The method comprises the following steps:

-   -   i. epoxy is mixed with conducting particles to form a matrix        with conducting particles    -   ii. the matrix is applied between surfaces that shall be        electrically and mechanically connected    -   iii. an electrical field in the range of 0.01 to 20 kV/cm is        applied over the matrix    -   iv. the matrix is cured, using e.g. UV light or heat

Example 1

This example concerns the preparation of a mixture of conductiveparticles and polymer matrix that in this example is an thermally curedpolymer adhesive; as well as determination of conductivity as a functionof particle load; and how the step-like increase in conductivity withincreasing particle load can be explained by formation of conductivepaths between particles when the contacts are formed with increasedparticle fraction.

This example concerns moreover the preparation of the same mixture whenthe particle load is low, for example 10 times less than the observedpercolation threshold, the limit where the isotropic non-aligned mixtureis not conductive; as well as the alignment of this mixture usingelectric field so that the aligned particles form conductive pathsresulting in a conductive material, whose conductivity is directional.The example, moreover, shows change of the viscosity of so obtainedmaterial, by curing, so that the alignment and directional conductivityobtained in the alignment step is maintained.

The employed conductive particles were CB from Alfa Aesar, CNC fromn-Tec AS (Norway) and iron oxide (FeO.Fe₂O₃) from Sigma-Aldrich.

The employed polymer matrix was a two component low viscosity adhesiveformed by combining Araldite® AY 105-1 (Huntsman Advanced MaterialsGmbH) with low viscosity epoxy resin with Ren® HY 5160 (Vantico AG).

The conductive particles were mixed in the adhesive by stirring for 30minutes. Due to the high viscosity of mixture, efficient mixing ispossible only up to 20 vol-%. of particles.

Estimated percolation threshold of these materials are at ˜2 vol-%. Themixtures are conductive above and insulators below this threshold. Theconductivity is due to the conductive particles and the polymer isessentially insulator.

To illustrate the benefit of alignment, the particle loads of 1/10 ofthe estimated percolation threshold were used.

FIG. 1 illustrates, using optical micrographs, the mixing of assembliesof 0.2 vol-% CNC particles dispersed into the example adhesive before(FIG. 1A) and after an electric field alignment and curing (FIG. 1B).

The scheme shows the applied alignment (out-of-plane) geometry (FIG.1C). This alignment geometry was used to cover conductive path distancesfrom 10 μm to 2 mm. For an out-of-plane alignment 2 mm×3 cm wide layerof material is injected between two metal electrodes with spacing of ≤2mm.

Mixture was aligned using an AC source. In this example the alignmentprocedure 1 kHz AC-field (0.6-4 kV/cm, rms value) was employed for >10minutes for >1 mm electrode spacing and <10 minutes for <1 mm electrodespacing.

FIG. 2 shows the conductivity as a function of alignment timeillustrating orders of magnitudes conductivity enhancement.

The curing was performed immediately afterwards at 100° C. for 6minutes.

The material remains aligned after curing and conductivity levelobtained by alignment is maintained.

Example 2

This example concerns versatile choice of alignment conditions andillustrates how the present invention can be employed not only withelectrodes connected to the orientation material but also withelectrodes electrically isolated from the material.

The procedure was otherwise similar to that in example 1, but instead ofhaving material directly connected to the alignment electrodes, theelectrodes were electrically disconnected from the material by aninsulating layer, for example by 0.127 mm Kapton® foils. Alignmentoccurred exactly as in Example 1.

This procedure allows removal of electrodes after alignment and thusfreestanding aligned film even in the case where the matrix is adhesive.The alignment also occurs if the electrodes do not touch the materialand so the alignment can be performed from the distance. When thematerial and electrodes are moved, continuous or stepwise, with respectto each others during the alignment, this allows continuous alignmentprocessing. Three possible options for the alignment settings areillustrated in FIG. 3 that shows aligned film with (A-B) and without(C-D) electrical contacts between electrodes (a) and material (b). Inthe case (A) the aligned film forms permanent connection between theelectrodes. In the case (B) the electrodes and material are only looselyjoined together and can be moved apart after alignment. In the case (C)there are insulating layers (c) between the material and electrodes andthey are easily moved apart after the alignment even in the case wherethe material is an adhesive. In this case the obtained material is amultilayer consisting of aligned layer (b) and two insulating layers (c)In the case (D) the alignment is carried out from the distance and themutual location of electrodes and film can be additionally moved duringthe alignment.

Example 3

This example concerns the applicability of the alignment method, the useof alignment for particular application of UV-curing. This emphasisesthe benefit of low particle fraction which makes the material moretransparent for UV light for curing.

The procedure was otherwise similar to that in example 1 or 2 but thethermally cured polymer matrix was replaced by UV-curable Dymax UltraLight-Weld® 3094 adhesive and the curing step was done by the UV-lightwith the wavelength 300-500 nm.

FIG. 4 illustrates the alignment of 0.2 vol-% CNC dispersion inout-of-plane geometry. The mixture was formed following the guideline ofexample 1 (FIG. 4a ) but spread on the alignment electrode using RKPrint Paint Applicator that uses a moving bird applicator to level theadhesive layer to the predetermined thickness (the idea is schematicallyillustrated in FIG. 4b ). This admixture was aligned following themethod outlined in example 2 but the upper electrode was not in contactwith the material by use of an insulating layer such as Kapton (FIG. 4c); this allows removal of electrodes after alignment and thusfreestanding aligned film even in the case where the matrix is adhesive.After alignment, the upper alignment electrode is removed and alignedadmixture cured by UV or blue light. (FIG. 4d ). The lower electrode canbe optionally removed (FIG. 4e ) to form a fully free-standing film.

FIG. 4 also gives the schematics of UV curing. Conductive particles aredispersed with UV-curable polymer matrix (a). This mixture is spread toform a predetermined layer on the substrate (that acts also as analignment electrode) using an applicator (b). The material is aligned byelectric field using lower electrode and another top-electrode that doesnot touch the material (c). The upper electrode is removed and thealigned mixture is cured using a light (UV/vis) source, which leads to asemi-freestanding aligned film (d). If required, the lower electrode canbe additionally removed leading to a fully free-standing aligned film(e).

Example 4

This example shows how the present invention can be employed withthermoplastic or thermotropic polymer matrix.

The procedure was otherwise similar to that in Example 1 or 2 butthermoplastic or thermotropic polymer is used instead of thermosetpolymer. In this example alignment was performed when the material wasfluid at elevated temperature above the melting point of material.Permanent alignment was achieved when the temperature of fluid matrixwith aligned particles was decreased below its glass transition ormelting point, which resulted in the stabilization of material.

The used matrix material was polyfluorene polymer (American Dye Source,with melting point at 180° C.)

Example 5

This example illustrates how the invention can be employed with polymermatrix and co-solvent.

The procedure was otherwise similar to that in examples 1, 2, 3, or 4but the polymer matrix contains solvent. The alignment was performedwith the presence of solvent and the solvent was evaporating off afteralignment. This can occur with or without curing of thermoset polymer orcooling thermoplastic or thermotropic polymer.

In the case of thermoset polymer matrix this solvent decreases theviscosity of matrix polymer. This means that the solvent acts asthinner. An example solvent in the thermocured polymer in example 1 isbenzylalcohol that is a good solvent for epoxy resin and hardener.

In the case of thermoplastic or thermotropic polymer matrix in example 1this solvent makes the mixture fluid already below the melting point ofmatrix and allows thus alignment at lower temperature. A possiblesolvent in example 4 is toluene that is a good solvent for polyfluorene.

Example 6

This example shows the robustness of the procedure and shows howelectric field heals macroscopic defects in a conductive particleadhesive mixture.

The materials and procedure was similar to that in examples 1, 2, 3, 4,or 5, but a macroscopic scratch defect was made by a sharp spike; andthe electric field was reapplied. FIG. 5a-e are optical micrographsshowing the healing of the scratch in the case of CNC particle mixture.

Example 7

This example concerns versatile choice of alignment geometries andillustrates how the invention can be employed not only in the geometryshown in Example 1 but also in (i) thin films and (ii) in in-planegeometry. This example underlines the generality of the method.

The material was the same and the procedure similar as in Example 1, butinstead of out-of-plane alignment geometry, in-plane alignment geometrywas used.

For the in-plane alignment ˜10 μm thick layer was spread either byspin-coating or by plastic spatula over 1 cm×1 cm area of metal fingergrid where the thickness and width of fingers, respectively, were 50-200nm and 2-10 μm. The spacing between fingers was 10-100 μm.

FIG. 6 illustrates aligned and cured conductive CNC adhesives inin-plane geometry. FIG. 6a shows an optical micrograph 0.2 vol-% alignedmaterial. Schematic (FIG. 6b ) illustrates the alignment setting. Inthis geometry the alignment occurs typically in seconds or tens ofseconds.

In another version the alignment electrodes were electrically insulatedfor example by SiO₂ layer following the idea of example 2. Alignment wasachieved exactly as without insulating layer.

Example 8

This example concerns versatile choice of alignment geometries andillustrates how the invention can be employed not only in theout-of-plane and in-plane geometries with flat well defined electrodesbut also when the geometry and electrode shape is arbitrary. Thisexample underlines the generality of the method. This also illustratesthat the alignment does not require a surface or interface parallel tothe emerging aligned pathways.

The materials were otherwise the same and the procedure similar as inExample 1, 2, 3, 4, or 5 but instead of out-of-plane or in-planealignment geometry and flat electrodes, arbitrary geometry and arbitraryelectrode shape were used. FIG. 7 shows an optical micrograph of alignedmaterial when arbitrary geometry and arbitrary electrode shapes havebeen used.

Example 9

This example concerns another feature of the invention, the reduction ofmatrix after alignment and stabilization. This illustrates how thepresent invention can be employed in (i) thin films and (ii) in in-planegeometry so that the outcome forms solitary network of aligned pureconductive particles or aligned channels with conductive core andinsulating mantle.

The material was otherwise the same and the procedure similar as inexample 1 but all or part of the matrix was removed from the aligned andcured film. In typical procedure the aligned and cured film was heatedat 450° C. from 10 minutes to 2 hours. As a result of this procedurestep, the thickness of matrix was greatly reduced between the conductivechannels and instead of a uniform film with aligned conductive channelsembedded into it, a film with distinctive solitary network was achieved(see FIG. 8).

This procedure can be performed similarly to the materials examplesshown in examples 1, 2, 3, 4, or 5. Alternative overall steps areillustrated in FIG. 9, which illustrates the steps to produce alignedconducting film. From left to right: Molecules are dispersed into fluidwhich can be thermoset, thermoplastic or lyotropic material. Thin filmof this dispersion is spread over a substrate. Aligned particle channelsforming conductive channels are formed by applying an electric field.Solid uniform film with aligned conductive channels is formed bychanging the viscosity. In the case of thermoset matrix this is achievedby curing the matrix polymer. In the case of thermoplastic matrix thisis achieved by decreasing the alignment temperature below a phasetransition such as melting point or glass transition of the matrix. Inthe lyotropic case the alignment is performed with the presence ofsolvent and the solidification obtained by evaporating solvent off. Anetwork of separated aligned wires may be formed by removing part or theentire matrix, for instance by a selective solvent or by pyrolysing apart of the solid matrix.

Example 10

This example concerns further versatility of the invention, the use ofelectric field alignment when preparing electrodes with very largecontact area dendrimer surface.

The procedure was otherwise similar to that in examples 1, 2, 3, 4, 5,7, 8, or 9 but the alignment was terminated before the chains reachedfrom electrode to electrode. FIG. 10 shows so obtained electrodes withdendritic surface.

The invention claimed is:
 1. A method for forming a body comprising amixture of a matrix and conductive particles having a low aspect ratio,the method comprising: a) providing a mixture comprising a matrixcapable of being stabilized and conductive particles; b) aligning theconductive particles into conductive pathways by applying an electricfield between alignment electrodes, wherein the electric field is in theorder of 0.1-20 kV/cm; c) stabilizing the mixture, and d) totally orpartly removing the matrix from the mixture, after stabilizing, whereinthe conductive particles are at least one infusible conductive particle,a metallic particle, a metal oxide particle, and a colloidal metalparticle.
 2. The method in accordance with claim 1, wherein one or moreof the alignment electrodes are not in direct contact with the mixtureduring the aligning.
 3. The method in accordance with claim 2, whereinone or more of the alignment electrodes are insulated from the mixture.4. The method in accordance with claim 1, wherein the alignmentelectrodes are in-plane, out-of-plane or arbitrary oriented in relationto the body.
 5. The method in accordance with claim 1, furthercomprising: second aligning the conductive particles into the conductivepathways by applying an electric field between the alignment electrodesto repair defective conductive pathways, wherein the electric fieldapplied is in the order of 0.1-20 kV/cm.
 6. The method in accordancewith claim 1, wherein the matrix is a UV curable polymer.
 7. The methodin accordance with claim 1, wherein the matrix is an adhesive.
 8. Themethod in accordance with claim 1, wherein the matrix is totally removedin d).
 9. The method in accordance with claim 1, wherein a concentrationof the conductive particles in the mixture is below a percolationthreshold.
 10. The method in accordance with claim 1, wherein one ormore of the electrodes are in contact with the mixture, and the aligningis interrupted before the conductive pathway has reached through themixture.
 11. The method in accordance with claim 1, wherein saidconductive particles have an aspect ratio ranging from 1-4.
 12. Themethod in accordance with claim 1, wherein said conductive particleshave an aspect ratio ranging from 1-5.
 13. The method in accordance withclaim 1, wherein said conductive particles have an aspect ratio rangingfrom 1-10.
 14. The method in accordance with claim 1, wherein saidconductive particles have an aspect ratio ranging from 1-20.
 15. Themethod in accordance with claim 1, wherein said electric field appliedis in the order of 0.1-5 kV/cm.
 16. The method in accordance with claim1, wherein said electric field applied is in the order of 0.1-1 kV/cm.17. The method in accordance with claim 1, wherein said electric fieldis an alternating filed having a frequency of 1-Hz to 10 kHz.
 18. Themethod in accordance with claim 1, wherein conductive particle is aninfusible conductive particle.
 19. The method in accordance with claim1, wherein the infusible conductive particle is a carbon particleselected from the group consisting of spherical carbon black, carboncones, carbon discs, and a mixture thereof.
 20. The method in accordancewith claim 1, wherein the conductive particles comprise a memberselected from the group consisting of a metallic particle, a metal oxideparticle, and a colloidal metal particle.
 21. The method in accordancewith claim 1, wherein the matrix is partly removed in d).
 22. A methodfor forming a body comprising a mixture of a matrix and conductiveparticles having a low aspect ratio, the method comprising: a) aligningthe conductive particles into conductive pathways by applying anelectric field between alignment electrodes to the mixture, wherein theelectric field is in the order of 0.1-20 kV/cm and the alignmentelectrodes are not in direct contact with the mixture during thealigning; and b) thereafter, stabilizing the mixture, and c) totally orpartly removing the matrix from the mixture, after the stabilizing,wherein a concentration of the conductive particles in the mixture isbelow a percolation threshold and wherein the conductive particles areat least one infusible conductive particle, a metallic particle, a metaloxide particle, and a colloidal metal particle.
 23. A method for forminga body comprising a mixture of a matrix and conductive particles, themethod comprising: a) providing a mixture comprising a matrix capable ofbeing stabilized and conductive particles; b) aligning the conductiveparticles into conductive pathways by applying an electric field betweenalignment electrodes, wherein the electric field is in the order of0.1-20 kV/cm; and c) stabilizing the mixture, and d) totally or partlyremoving the matrix from the mixture, after the stabilizing, wherein theconductive particles have an aspect ratio ranging from 1-20.
 24. Themethod in accordance with claim 23, wherein one or more of the alignmentelectrodes are not in direct contact with the mixture during thealigning.
 25. The method in accordance with claim 24, wherein one ormore of the alignment electrodes are insulated from the mixture.
 26. Themethod in accordance with claim 23, wherein the alignment electrodes arein-plane, out-of-plane or arbitrary oriented in relation to the body.27. The method in accordance with claim 23, further comprising: secondaligning the conductive particles into the conductive pathways byapplying an electric field between the alignment electrodes to repairdefective conductive pathways, wherein the electric field applied is inthe order of 0.1-20 kV/cm.
 28. The method in accordance with claim 23,wherein the matrix is a UV curable polymer.
 29. The method in accordancewith claim 23, wherein the matrix is an adhesive.
 30. The method inaccordance with claim 23, wherein the matrix is totally or partlyremoved in d) from the mixture after the stabilizing.
 31. The method inaccordance with claim 23, wherein a concentration of the conductiveparticles in the mixture is below a percolation threshold.
 32. Themethod in accordance with claim 23, wherein one or more of theelectrodes are in contact with the mixture, and the aligning isinterrupted before the conductive pathway has reached through themixture.
 33. The method in accordance with claim 23, wherein saidconductive particles have an aspect ratio ranging from 1-4.
 34. Themethod in accordance with claim 23, wherein said conductive particleshave an aspect ratio ranging from 1-5.
 35. The method in accordance withclaim 23, wherein said conductive particles have an aspect ratio rangingfrom 1-10.
 36. The method in accordance with claim 23, wherein saidelectric field applied is in the order of 0.1-5 kV/cm.
 37. The method inaccordance with claim 23, wherein said electric field applied is in theorder of 0.1-1 kV/cm.
 38. The method in accordance with claim 23,wherein said electric field is an alternating filed having a frequencyof 1-Hz to 10 kHz.
 39. The method according to claim 23, wherein theconductive particles are infusible conductive particles.
 40. The methodin accordance with claim 23, wherein the matrix is partly removed in d).41. A method for forming a body comprising a mixture of a matrix andconductive particles having a low aspect ratio, the method comprising:a) aligning the conductive particles into conductive pathways byapplying an electric field between alignment electrodes to the mixture,wherein the electric field is in the order of 0.1-20 kV/cm and thealignment electrodes are not in direct contact with the mixture duringthe aligning; and b) thereafter, stabilizing the mixture, and c) totallyor partly removing the matrix from the mixture, after the stabilizing,wherein a concentration of the conductive particles in the mixture isbelow a percolation threshold and wherein the conductive particles havean aspect ratio ranging from 1-20.
 42. The method according to claim 41,wherein the conductive particles are infusible conductive particles.